Systems and methods for making encapsulated hourglass shaped stents

ABSTRACT

Systems and methods for the manufacture of an hourglass shaped stent-graft assembly comprising an hourglass shaped stent, graft layers, and an assembly mandrel having an hourglass shaped mandrel portion. Hourglass shaped stent may have superelastic and self-expanding properties. Hourglass shaped stent may be encapsulated using hourglass shaped mandrel assembly coupled to a dilatation mandrel used for depositing graft layers upon hourglass shaped mandrel assembly. Hourglass shaped mandrel assembly may have removably coupled conical portions. The stent-graft assembly may be compressed and heated to form a monolithic layer of biocompatible material. Encapsulated hourglass shaped stents may be used to treat subjects suffering from heart failure by implanting the encapsulated stent securely in the atrial septum to allow blood flow from the left atrium to the right atrium when blood pressure in the left atrium exceeds that on the right atrium. The encapsulated stents may also be used to treat pulmonary hypertension.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation patent application of U.S. patentapplication Ser. No. 15/798,250, filed Oct. 30, 2017, now U.S. Pat. No.11,109,988, which is a continuation patent application of U.S. patentapplication Ser. No. 15/608,948, filed May 30, 2017, which claims thebenefit of priority of U.S. Provisional Patent Application Ser. No.62/343,658, filed May 31, 2016, the entire contents of each of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This application relates to systems and methods for the manufacture ofhourglass or “diabolo” shaped encapsulated stents for treatingcongestive heart failure and other disorders treated with encapsulatedhourglass shaped stents.

BACKGROUND

Heart failure is the physiological state in which cardiac output isinsufficient to meet the needs of the body and the lungs. CongestiveHeart Failure (CHF) occurs when cardiac output is relatively low due toreduced contractility or heart muscle thickening or stiffness. There aremany possible underlying causes of CHF, including myocardial infarction,coronary artery disease, valvular disease, and myocarditis.

CHF is associated with neurohormonal activation and alterations inautonomic control. Although these compensatory neurohormonal mechanismsprovide valuable support for the heart under normal physiologicalcircumstances, they also have a fundamental role in the development andsubsequent progression of CHF. For example, one of the body's maincompensatory mechanisms for reduced blood flow in CHF is to increase theamount of salt and water retained by the kidneys. Retaining salt andwater, instead of excreting it into the urine, increases the volume ofblood in the bloodstream and helps to maintain blood pressure. However,the larger volume of blood also stretches the heart muscle, enlargingthe heart chambers, particularly the ventricles. At a certain amount ofstretching, the hearts contractions become weakened, and the heartfailure worsens. Another compensatory mechanism is vasoconstriction ofthe arterial system. This mechanism, like salt and water retention,raises the blood pressure to help maintain adequate perfusion.

In low ejection fraction (EF) heart failure, high pressures in the heartresult from the body's attempt to maintain the high pressures needed foradequate peripheral perfusion. However, the heart weakens as a result ofthe high pressures, aggravating the disorder. Pressure in the leftatrium may exceed 25 mmHg, at which stage, fluids from the blood flowingthrough the pulmonary circulatory system flow out of the interstitialspaces and into the alveoli, causing pulmonary edema and lungcongestion.

CHF is generally classified as either Heart Failure with reducedEjection Fraction (HFrEF) or Heart Failure with preserved EjectionFraction (HFpEF). In HFrEF, the pumping action of the heart is reducedor weakened. A common clinical measurement is the ejection fraction,which is a function of the blood ejected out of the left ventricle(stroke volume), divided by the maximum volume remaining in the leftventricle at the end of diastole or relaxation phase (End DiastolicVolume). A normal ejection fraction is greater than 50%. HFrEF has adecreased ejection fraction of less than 40%. A patient with HFrEF mayusually have a larger left ventricle because of a phenomenon calledcardiac remodeling that occurs secondarily to the higher ventricularpressures.

In HFpEF, the heart generally contracts normally, with a normal ejectionfraction, but is stiffer, or less compliant, than a healthy heart wouldbe when relaxing and filling with blood. This stiffness may impede bloodfrom filling the heart, and produce backup into the lungs, which mayresult in pulmonary venous hypertension and lung edema. HFpEF is morecommon in patients older than 75 years, especially in women with highblood pressure.

Both variants of CHF have been treated using pharmacological approaches,which typically involve the use of vasodilators for reducing theworkload of the heart by reducing systemic vascular resistance, as wellas diuretics, which inhibit fluid accumulation and edema formation, andreduce cardiac filling pressure. However, pharmacological approaches arenot always successful, as some people may be resistant or experiencesignificant side effects

In more severe cases of CHF, assist devices such as mechanical pumpshave been used to reduce the load on the heart by performing all or partof the pumping function normally done by the heart. Chronic leftventricular assist devices (LVAD), and cardiac transplantation, oftenare used as measures of last resort. However, such assist devices aretypically intended to improve the pumping capacity of the heart, toincrease cardiac output to levels compatible with normal life, and tosustain the patient until a donor heart for transplantation becomesavailable. Such mechanical devices enable propulsion of significantvolumes of blood (liters/min), but are limited by a need for a powersupply, relatively large pumps, and the risk of hemolysis, thrombusformation, and infection. In addition to assist devices, surgicalapproaches such as dynamic cardiomyoplasty or the Batista partial leftventriculectomy may also be used in severe cases. However theseapproaches are highly invasive and have the general risks associatedwith highly invasive surgical procedures.

U.S. Pat. No. 6,468,303 to Amplatz et al. describes a collapsiblemedical device and associated method for shunting selected organs andvessels. Amplatz describes that the device may be suitable to shunt aseptal defect of a patient's heart, for example, by creating a shunt inthe atrial septum of a neonate with hypoplastic left heart syndrome(HLHS). Amplatz describes that increasing mixing of pulmonary andsystemic venous blood improves oxygen saturation. Amplatz describes thatdepending on the hemodynamics, the shunting passage can later be closedby an occluding device. However, Amplatz is silent on the treatment ofCHF or the reduction of left atrial pressure, and is also silent onmeans for regulating the rate of blood flow through the device.

U.S. Pat. No. 8,070,708 to Rottenberg describes a method and device forcontrolling in-vivo pressure in the body, and in particular, the heart.The device described in Rottenberg involves a shunt to be positionedbetween two or more lumens in the body to permit fluid to flow betweenthe two lumens. The Rottenberg patent further describes that anadjustable regulation mechanism may be configured to cover an opening ofthe shunt to regulate flow between the two lumens. The shunt isconfigured such that the flow permitted is related to a pressuredifference between the two lumens. The adjustable regulation mechanismmay be remotely activated. The Rottenberg patent describes that thedevice described may be used to treat CHF by controlling pressuredifference between the left atrium and the right atrium. WhileRottenberg describes a mechanism for treating CHF by controlling theflow between the left atrium and the right atrium, it does not describethe encapsulation of an hourglass shaped stent.

U.S. Patent Publication No. 2005/0165344 to Dobak, III describes anapparatus for treating heart failure that includes a conduit positionedin a hole in the atrial septum of the heart, to allow flow from the leftatrium into the right atrium. Dobak describes that the shunting of bloodwill reduce left atrial pressures, thereby preventing pulmonary edemaand progressive left ventricular dysfunction, and reducing LVEDP. Dobakdescribes that the conduit may include a self-expandable tube withretention struts, such as metallic arms that exert a slight force on theatrial septum on both sides and pinch or clamp the valve to the septum,and a one-way valve member, such as a tilting disk, bileaflet design, ora flap valve formed of fixed animal pericardial tissue. However, Dobakstates that a valved design may not be optimal due to a risk of bloodstasis and thrombus formation on the valve, and that valves can alsodamage blood components due to turbulent flow effects. Dobak does notprovide any specific guidance on how to avoid such problems.

U.S. Pat. No. 9,034,034 to Nitzan, incorporated herein by reference,describes a device for regulating blood pressure between a patient'sleft atrium and right atrium which comprises an hourglass-shaped stenthaving a neck region and first and second flared end regions, the neckregion disposed between the first and second end regions and configuredto engage the fossa ovalis of the patient's atrial septum. Nitzandescribes that the hourglass shaped stent is also encapsulated with abiocompatible material. While Nitzan describes a method for themanufacture of an hourglass shaped stent for the treatment of CHF,Nitzan is silent on the method of encapsulating the stent.

U.S. Pat. No. 6,214,039 to Banas, incorporated herein by reference,describes a method for covering a radially endoluminal stent. In themethod described by Banas, the encapsulated stent is assembled byjoining a dilation mandrel and a stent mandrel, placing the graft on thedilation mandrel where it is radially expanded, and passing the expandedgraft over the stent that is positioned on the stent mandrel. WhileBanas describes a method for encapsulating a cylindrical stent, themethod in Banas does not describe encapsulation of an hourglass shapedstent intended for treatment of CHF. The method for assembling thecovered stent and mandrel assembly described in Banas would beinappropriate for assembly of an hourglass stent described in Nitzan.

U.S. Pat. No. 6,797,217 to McCrea, incorporated herein by reference,describes a method for encapsulating stent grafts. McCrea describesmethods for encapsulating an endoluminal stent fabricated from a shapememory alloy. The Method described by McCrea involves an endoluminalstent encapsulated in an ePTFE covering which circumferentially coversboth the luminal and abluminal walls along at least a portion of thelongitudinal extent of the endoluminal stent. McCrea further describesapplying pressure to the stent-graft assembly and heating the assemblyto complete the encapsulation. While McCrea describes an encapsulatedendoluminal stent, it does not describe the encapsulation of anhourglass shaped stent for the treatment of CHF.

In view of the above-noted drawbacks of previously known systems, itwould be desirable to provide systems and methods of manufacture ofencapsulated hourglass shaped stents for treating congestive heartfailure and other disorders treated with hourglass shaped stent-graftassemblies.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of previously-knownsystems and methods by providing systems and methods for makingencapsulated hourglass shaped stents for treating CHF and otherconditions benefited by encapsulated hourglass shaped stents such aspulmonary hypertension. The hourglass or “diabolo” shaped stents areconfigured to be encapsulated using a mandrel assembly.

In accordance with one aspect, a method for making an encapsulatedstent-graft may involve, providing a mandrel having a first conicalregion with a first apex and a second conical region with a second apex,placing an expandable stent having an hourglass shape in an expandedform on the mandrel so that a first flared end region of the expandablestent conforms to the first conical region and a second flared endregion of the expandable stent conforms to the second conical region,associating a biocompatible material with the expandable stent to form astent-graft assembly, and compressing the stent-graft assembly againstthe mandrel to form the encapsulated stent-graft. The first conicalregion and the second conical region may be aligned so that the firstand second apexes contact one another.

The biocompatible material may have first and second ends andassociating the biocompatible material with the expandable stentinvolves placing the biocompatible material within a lumen of theexpandable stent. The method may further include placing a secondbiocompatible material over the expandable stent. Compressing thestent-graft assembly may involve winding a layer of tape over thebiocompatible material to compress the stent-graft assembly against themandrel. The expandable stent may include through-wall openings, and themethod may further involve heating the stent-graft assembly to cause thebiocompatible material and the second biocompatible material to bond toone another through the through-wall openings. Heating the stent-graftassembly may cause the biocompatible material and the secondbiocompatible material to become sintered together to form a monolithiclayer of biocompatible material. The method may further involve applyinga layer of Fluorinated Ethylene Propylene (FEP) to biocompatiblematerial or second biocompatible material. The biocompatible materialmay be pre-formed. The method may further involve manipulating theencapsulated stent-graft to a compressed shape and loading theencapsulated stent-graft into a delivery sheath. A first end diameter ofthe expandable stent may be different in size from a second enddiameter. The mandrel may have a neck region disposed between a firstconical region and a second conical region and the mandrel may beconfigured to be removably uncoupled at the neck region into a firsthalf having at least the first conical region and a second half havingat least the second conical region.

In accordance with another aspect, a method for making an encapsulatedstent-graft may involve providing a mandrel assembly having anasymmetric shape, providing an expandable stent in an expanded form,coupling a biocompatible material to the expandable stent to form astent-graft assembly, and compressing the stent-graft assembly on themandrel assembly to form the encapsulated stent-graft. The expandablestent may be configured to conform to the asymmetric shape formed by themandrel assembly.

The expandable stent and the biocompatible material may be coupled onthe mandrel assembly or before placement on the mandrel assembly. Themethod may further involve coupling a second biocompatible material toan opposing surface of the expandable stent to form the stent-graftassembly. The second biocompatible material may be formed of a same ordifferent material as the biocompatible material. The mandrel assemblymay include a first mandrel and a second mandrel, and the method mayfurther involve, positioning the first mandrel within the first end ofthe expandable stent such that a portion of the second biocompatiblematerial is positioned between the first mandrel and the expandablestent, and positioning the second mandrel within the second end of theexpandable stent such that a portion of the second biocompatiblematerial is positioned between the second mandrel and the expandablestent. The biocompatible material may be a pre-formed biocompatiblegraft layer having the expandable stent. The pre-formed biocompatiblegraft layer may engage the expandable stent on the mandrel assembly.

In accordance with yet another aspect, a method for making anencapsulated stent-graft may involve providing an asymmetrical stent,placing a first biocompatible material over the asymmetrical stent,providing a second biocompatible material for placement within theasymmetrical stent, inserting a balloon catheter having an inflatableballoon within the asymmetrical stent in a deflated state such that thesecond biocompatible material is between the asymmetrical stent and theinflatable balloon, and inflating the inflatable balloon to an inflatedstate conforming to the shape of the asymmetrical stent, thereby causingthe second biocompatible material to engage with the asymmetrical stentto form the encapsulated stent-graft.

The method may further involve controlling the pressure within theballoon to achieve a desired adhesion between the first biocompatiblematerial and the second biocompatible material. The method may furtherinvolve controlling the pressure within the balloon to achieve a desiredinter-nodal-distance of the graft material. The second biocompatiblematerial may be placed within the asymmetrical stent prior to insertingthe balloon catheter within the asymmetrical stent. The secondbiocompatible material may be disposed on the inflatable balloon, andinflating the inflatable balloon may cause the second biocompatiblematerial disposed on the inflatable balloon to contact and inner surfaceof the asymmetrical stent thereby engaging the second biocompatiblematerial with the asymmetrical stent.

In accordance with yet another aspect, a method for making anencapsulated stent-graft may involve providing a funnel having a largeend and a small end, placing an asymmetric stent with a first end, asecond end, an exterior surface and an interior surface within the largeend of the funnel, placing a biocompatible tube over the small end ofthe funnel, the biocompatible tube having a stent receiving portion anda remaining portion, advancing the asymmetric stent through the funneland out the small end of the funnel, thereby depositing the asymmetricstent into the biocompatible tube such that the stent is positionedwithin the stent receiving portion of the biocompatible tube, therebyengaging an exterior surface of the asymmetric stent with thebiocompatible tube, pulling the remaining portion of the biocompatibletube through the first end of the asymmetric stent and out the secondend, introducing a first mandrel having a shape similar to the firstside of the asymmetric stent into the first side of asymmetric stentthereby engaging the interior surface of the first side of theasymmetric stent with a portion of the remaining portion of thebiocompatible tube, and introducing a second mandrel having a shapesimilar to the second side of the asymmetric stent into the second sideof the asymmetric stent thereby engaging the interior surface of thesecond side of the asymmetric stent with a portion of the remainingportion of the biocompatible tube.

In accordance with yet another aspect, an hourglass shaped mandrelassembly for making an encapsulated stent-graft may involve a firstportion having at least a first conical region having a flared end witha first diameter and an apex end with a second diameter, a secondportion having at least a second conical region having a flared end withthird diameter and an apex end with a fourth diameter, and a taperedregion coupled to the flared end of the first portion and extending awayfrom the flared end of the first portion. The tapered region may have aflared end with a fifth diameter and a tapered end with a sixth diametersuch that the fifth diameter is equal to the first diameter and thesixth diameter is smaller than the fifth diameter. The first conicalregion of the first portion and the second conical region of the secondportion may be aligned so that apexes of the first portion and secondportion are contacting one another. The hourglass shaped mandrelassembly may further include a neck region positioned between the apexend of the first portion and the apex end of the second portion suchthat the neck region is affixed to at least the first portion or thesecond portion. The first portion and the second portion may beremovably coupled at the apex end of the first portion and the apex endof the second portion. The hourglass shaped mandrel may be configured toexpand radially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side view of hourglass shaped stent constructed in accordancewith the methods of the present invention.

FIG. 2 is a cross-section view of hourglass shaped stent encapsulatedwith first and second graft layers.

FIG. 3 is a partially exploded side view of assembly apparatus formanufacturing hourglass stent-graft assembly in accordance with themethods of the present invention.

FIG. 4 is a side view of hourglass shaped mandrel assembly section ofassembly apparatus for manufacturing hourglass shaped stent-graftassembly in accordance with the methods of the present invention.

FIG. 5 is a side view of assembly apparatus engaged with first grafttube at the tapered region.

FIG. 6 is a side view of assembly apparatus engaged with first grafttube over hourglass shaped mandrel assembly section.

FIG. 7 is a side view of first graft layer disposed over hourglassshaped mandrel assembly section of assembly apparatus.

FIGS. 8A-8C are side views of assembly apparatus engaged with firstgraft layer and hourglass shaped stent.

FIG. 9 is a side view of assembly apparatus engaged with second grafttube at the tapered region.

FIG. 10 is a side view of assembly apparatus engaged with second grafttube over hourglass shaped mandrel assembly section of assemblyapparatus.

FIG. 11 is a side view of stent-graft disposed over hourglass shapedmandrel assembly section.

FIGS. 12A-12D are side views sequentially illustrating an encapsulationtechnique involving a male and female mandrel.

FIGS. 13A-13E are side views sequentially illustrating an encapsulationtechnique involving pre-shaped grafts and a male and female mandrel.

FIGS. 14A-14D are side views sequentially illustrating an encapsulationtechnique involving an inflatable balloon.

FIGS. 15A-15F are side views sequentially illustrating an encapsulationtechnique involving a funnel and a male and female mandrel.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to systems and methodsfor the manufacture of hourglass or “diabolo” shaped stents encapsulatedwith biocompatible material for treating subjects suffering fromcongestive heart failure (CHF) or alternatively pulmonary hypertension.The hourglass or “diabolo” shaped stents are configured to beencapsulated using an hourglass shaped mandrel assembly having adilation portion and two conical regions that may be removably coupled.The hourglass shaped stents may be specifically configured to be lodgedsecurely in the atrial septum, preferably the fossa ovalis, to allowblood flow from the left atrium to the right when blood pressure in theleft atrium exceeds that on the right atrium. The resulting encapsulatedstents are particularly useful for the purpose of inter-atrial shuntingas they provide long-term patency and prevent tissue ingrowth within thelumen of the encapsulated stent. However, it is understood that thesystems and methods described herein may also be applicable to otherconditions benefited from an encapsulated hourglass shaped stent such aspulmonary hypertension wherein the encapsulated hourglass shaped stentis used as a right-to-left shunt.

Referring now to FIG. 1, stent 110 is illustrated. Stent 110 ishourglass or “diabolo” shaped and may be radially self-expandable.Alternatively, stent 110 may be expandable but not self-expandable. Forexample, stent 110 may be balloon expandable. Stent 110 has threegeneral regions: first flared end region 102, second end flared region106, and neck region 104 disposed between the first and second flaredend regions. First flared end region 102 has first end region diameterD1, second flared end region 106 has second end region diameter D2, andneck region 104 has neck diameter D3. As shown in FIG. 1, neck region104 of stent 110 is significantly narrower than flared end regions 102and 106. Also shown in FIG. 1, stent 110 may be asymmetric. For example,stent 110 may be asymmetric to take advantage of the natural features ofthe atrial septum of the heart as well as the left and right atriumcavities. Alternatively, hourglass shaped stent 110 may be symmetricwith the first end region diameter D1 being equal to the second endregion diameter D2. First flared end region 102 and second flared endregion 106 also may have either straight or curved profiles or both. Forexample, strut 111 has a straight profile and strut 108 has a curvedprofile. Additionally, first flared end region 102 and second flared endregion 106 may assume any angular position consistent with thehour-glass configuration.

Stent 110 is preferably comprised of a self-expanding material havingsuperelastic properties. For example, a shape-memory metal such asnickel titanium (NiTi), also known as NITINOL may be used. Othersuitable materials known in the art of deformable stents forpercutaneous implantation may alternatively be used such as other shapememory alloys, self-expanding materials, superelastic materials,polymers, and the like. The tube may be laser-cut to define a pluralityof struts and connecting members. For example, as illustrated in FIG. 1,the tube may be laser-cut to define a plurality of sinusoidal ringsconnected by longitudinally extending struts. Struts 108 and 111 andsinusoidal rings 112-116 illustrated in FIG. 1 may be laser cut to forman integral piece of unitary construction. Alternatively, struts 111 andsinusoidal rings 112-116 may be separately defined to form differentpieces of shape-memory metal and subsequently coupled together to formstent 110. The stent may also be electropolished to reducethrombogenicity.

Stent 110 may be expanded on a mandrel to define first end region 102,second end region 106, and neck region 104. The expanded stent then maybe heated to set the shape of stent 110. The stent may be expanded on amandrel in accordance with the teachings of U.S. Pat. No. 9,034,034 toNitzan, incorporated herein. In one example, stent 110 is formed from atube of NITINOL, shaped using a shape mandrel, and placed into an ovenfor 11 minutes at 530° C. to set the shape. The mandrel disclosed inFIGS. 3-4 may be configured as a shaping mandrel to set the shape ofstent 110 or, alternatively, a different mandrel may be used as theshaping mandrel.

Referring now to FIG. 2, stent 110 is at least partially covered withbiocompatible material, as shown in FIG. 2, to create stent-graftassembly 120. Biocompatible material may be expandedpolytetrafluoroethylene (ePTFE), silicone, polycarbonate urethane,DACRON (polyethylene terephthalate), Ultra High Molecular WeightPolyethylene (UHMWPE), or polyurethane, or of a natural material such aspericardial tissue, e.g., from an equine, bovine, or porcine source orhuman tissue such as human placenta or other human tissues. Thebiocompatible material is preferably smooth so as to inhibit thrombusformation, and optionally may be impregnated with carbon so as topromote tissue ingrowth. Alternatively, to promote tissue ingrowth andendothelization, the biocompatible material may form a mesh-likestructure. The biocompatible material may be pre-shaped using adedicated pre-shaping mandrel and heat treatment to simplify themounting of the biocompatible material on an encapsulation mandrel, asdiscussed in detail below. Pre-shaping the biocompatible material hasbeen shown to simplify the handling and mounting of the biocompatiblematerial on the mandrel, thereby reducing stretching and the risk fortears in the biocompatible material and may be especially beneficial forencapsulating asymmetrical stents. Portions of stent 110 such as firstflared end region 102 may not be covered with the biocompatiblematerial.

Generally, the stent is positioned between a first and second layer ofgraft material by covering an inner surface of stent 121 with firstgraft layer 170, and covering the outer surface of stent 123 with secondgraft layer 190. First graft layer 170 and second graft layer 190 eachmay have a first end and a second end and may have lengths that areabout equal. Alternatively, first graft layer 170 and second graft layer190 may have different lengths. Stent 110 may have a length that isshorter than the length of first graft layer 170 and second graft layer190. In other embodiments, stent 110 may have a length that is longerthan the length of first graft layer 170 and/or second graft layer 190.As discussed in detail below, the graft layers may be securely bondedtogether to form a monolithic layer of biocompatible material. Forexample, first and second graft tubes may be sintered together to form astrong, smooth, substantially continuous coating that covers the innerand outer surfaces of the stent. Portions of the coating then may beremoved as desired from selected portions of the stent usinglaser-cutting or mechanical cutting, for example.

In a preferred embodiment, stent 110 is encapsulated with ePTFE. It willbe understood by those skilled in the art that ePTFE materials have acharacteristic microstructure consisting of nodes and fibrils, with thefibrils orientation being substantially parallel to the axis oflongitudinal expansion. Expanded polytetrafluoroethylene materials aremade by ram extruding a compressed billet of particulatepolytetrafluoroethylene and extrusion lubricant through an extrusion dieto form sheet or tubular extrudates. The extrudate is thenlongitudinally expanded to form the node-fibril microstructure andheated to a temperature at or above the crystalline melt point ofpolytetrafluoroethylene, i.e., 327° C., for a period of time sufficientto sinter the ePTFE material. Heating may take place in a vacuum chamberto prevent oxidation of the stent. Alternatively, heating may take placein a nitrogen rich environment. A furnace may be used to heat thestent-graft assembly. Alternatively, or in addition to, the mandrel uponwhich the stent-graft assembly rests may be a heat source used to heatthe stent-graft assembly.

FIGS. 3-11 generally illustrate one method of making stent-graftassembly 120, as depicted in FIGS. 1-2. FIG. 3 is a partially explodedview of assembly apparatus 130. Assembly apparatus 130 may comprisetapered dilation mandrel 131, stent retaining mandrel 134 and stentenclosing mandrel 138. Tapered dilation mandrel 131 comprises first end132 having a taper diameter and second end 133 wherein the diameter ofsecond end 133 is greater than the taper diameter. Where othertechniques are used to dilate stent 110 and biocompatible graftmaterial, tapered dilation mandrel 131 may not be necessary and thusassembly apparatus 130 may comprise stent retaining mandrel 134 andstent enclosing mandrel 138.

Stent retaining mandrel 134 may be permanently affixed to second end 133of tapered dilation mandrel 131 or alternatively may be removablycoupled to tapered dilation mandrel. For example, stent retainingmandrel 134 may be screwed into tapered dilation mandrel 131 using ascrew extending from stent retaining mandrel 134 and a threaded insertembedded into tapered dilation mandrel 131. However, it will beunderstood by those in the art that couplings are interchangeable andmay be any of a wide variety of suitable couplings.

Stent retaining mandrel 134 may comprise a conical region defined bylarge diameter end 135 and an apex end 136. Large diameter end 135 maybe equal in diameter with second end 133 of tapered dilation mandrel131, and larger in diameter than apex end 136. It is understood thatstent retaining mandrel 134 may alternatively be other shapes includingnon-conical shapes. Stent retaining mandrel 134 may optionallyincorporate neck region 137. Neck region 137 may extend from apex end136, as shown in FIG. 3, and may have the same diameter as apex end 136.Alternatively, neck region 137 may extend from stent enclosing mandrel138.

Stent enclosing mandrel 138 is removably coupled to stent retainingmandrel 134. For example, stent enclosing mandrel 138 may be screwedinto stent retaining mandrel 134 using screw 139 extending from stentenclosing mandrel 138 and threaded insert 140 embedded into stentretaining mandrel 134. Alternatively, screw 139 may extend from stentretaining mandrel 134 and threaded insert may be embedded into stentenclosing mandrel 138. While the figures depict threaded coupling, itwill be understood by those in the art that the couplings areinterchangeable and may be any of a wide variety of suitable couplings.In another example, stent retaining mandrel 134 may be a female mandrelhaving a receiving portion and stent enclosing mandrel 138 may be a malemandrel having a protruding portion. However, it is understood thatstent retaining mandrel 134 may be a male mandrel having a protrudingportion and stent enclosing mandrel 138 may be a female mandrel having areceiving portion.

Stent enclosing mandrel 138 may comprise a conical region defined bylarge diameter end 142 and an apex end 141, wherein large diameter end142 is larger in diameter than apex end 141. It is understood that stentenclosing mandrel 138 alternatively take other shapes includingnon-conical shapes. Stent enclosing mandrel 138 may be permanentlyaffixed to handle segment 144 at large diameter end 142. Alternatively,stent enclosing mandrel 138 may be removably coupled to handle segment144. Where stent enclosing mandrel 138 is removably coupled to handlesegment 144, handle segment 144 may be removed and replaced with a tapermandrel segment similar to taper dilation mandrel 131, as shown in FIG.8C.

Referring to FIG. 4, when coupled together, stent retaining mandrel 134and stent enclosing mandrel 138 form hourglass shaped mandrel assembly143. Hourglass shaped mandrel assembly 143 is configured such that theconical region of stent retaining mandrel 134 is oriented toward theconical region of stent enclosing mandrel 138, wherein apex end 136 ofstent retaining mandrel 138 having extending neck region 137 is incontact with apex end 141 of stent enclosing mandrel 138. Neck region137 is configured to conform to the diameter of apex end 136 of stentretaining mandrel 138 and apex end 141 of stent enclosing mandrel 138,whether or not apex end 141 and apex end 136 are equal in diameter. Neckregion 137 may vary in diameter or may be eliminated entirely.

The size and shape of hourglass shaped mandrel assembly 143 andspecifically the size of the conical regions of stent retaining mandrel134 and stent enclosing mandrel 138 preferably correspond to the sizeand shape of flared end region 102, neck region 104 and second flaredend region 106 of stent 110. Hourglass shaped mandrel assembly 143 maybe asymmetrical such that diameter D4 of large diameter end 135 isdifferent than diameter D5 of large diameter end 142. Alternatively,diameter D4 and diameter D5 may be the same. Similarly, angle θ1 andangle θ2 may be different, resulting in an asymmetrical mandrel, or maybe the same. Angle θ1 and angle θ2 also may vary along the length ofhourglass shaped mandrel assembly 143 to better conform to stent 110.While neck diameter D6 may vary at different points along neck region137, diameter at neck region 137 is at all times smaller than diameterD4 and D5.

FIGS. 5-7, represents sequential views of first graft tube 122 beingloaded onto the tapered dilation mandrel 131 and being concentricallyengaged about hourglass shaped assembly 143 in an exemplary sequence.Engagement of first graft tube 122 over tapered dilation mandrel 131 maybe facilitated by forming tabs on first end 153 of first graft tube 122by cutting longitudinal slits (not shown) along diametrically opposingsides of the graft tube. The tabs can then be used to retain first grafttube 122 while axial force 150 is applied to assembly apparatus 130.Alternatively, the tabs may be used to manually pull first graft tube122 over tapered dilation mandrel 131 and hourglass shaped mandrelassembly 143. To prevent formation of seams or wrinkles, it is importantto avoid applying torsional forces to graft tubes by twisting the graftduring engagement of the graft member onto the assembly apparatus.Cutting crevice 151 and 152 may be incorporated into stent retainingmandrel 134 and stent enclosing mandrel 138 to provide a guidingindentation for a cutting element to cut first graft tube 122 and secondgraft tube 124.

Referring now to FIG. 5, first graft tube 122 may be engaged withtapered dilatation mandrel 131 by applying an axial force 150 toassembly apparatus 130 which causes the tapered dilatation mandrel topass into and through lumen 154 of first graft tube 122. As first grafttube 122 passes over second end 133 of tapered dilatation mandrel 131,the inner diameter of first graft first 122 is expanded radially to thatof the outer diameter of second end 133 of tapered dilation mandrel 131.As first graft tube 122 is moved axially over large diameter end 135 ofstent retaining mandrel 134 the inner diameter of first graft tube 122is greater than the outside diameter of hourglass shaped mandrelassembly 143. Axial force 150 is applied until first end 153 of firstgraft tube 122 is near large diameter end 142 of stent enclosing mandrel138. As first graft tube moves axially over second end 133 of tapereddilatation mandrel 131 and is positioned over hourglass shaped mandrelassembly 143, first graft tube 122 undergoes radial recoil so that theinner diameter of first graft tube 122 reduces until it's met withresistance from hourglass shaped mandrel 143. As illustrated in FIG. 6,first graft tube 122 has radially recoiled onto hourglass shaped mandrelassembly 143 as well as into cutting crevices 151 and 152.

FIGS. 6 and 7 illustrate the steps for separating first graft tube 122and depositing graft layer 170 upon hourglass shaped mandrel 143.Cutting blades 160 and 161 may be used to make circumferential cuts infirst graft tube 122 near the large diameter ends of stent retainingmandrel 134 and stent enclosing mandrel 138. For example, cutting bladesmay make circumferential cuts at the position of cutting crevices 151and 152. Cutting crevices 151 and 152 are positioned at a length longerthan the length of stent 110 to account for recoil of graft materialafter being cut. Alternatively, where the stent is only partiallyencapsulated, cutting crevices 151 and 152 may be positioned at a lengthshorter than the length of stent 110. After cutting first graft tube 122with cutting blades 160 and 161, first graft layer 170 is deposited ontostent 110. Alternatively, only cutting crevice 151 and cutting blade 160may be used to create a circumferential cut near the large diameter endof stent retaining mandrel 134. In this manner first end 153 of firstgraft tube 122 having tabs at the end, may serve as one end of firstgraft layer 170. First graft layer 170 has a length longer than stent110. As such, a section of first graft layer 170 extends beyond opposingends of stent 110. After removing excess grafting material, first graftlayer 170 remains on the assembly apparatus and covers hourglass shapedmandrel assembly 143. Tape may be applied to first graft layer 170 tosecure graft layer 170 to stent retaining mandrel 134. Upon depositingfirst graft layer 170 on hourglass shaped mandrel assembly 143, anoptional step involves applying a layer of Fluorinated EthylenePropylene (FEP), or any other adhesive material, to first graft layer170 for improving adhesion during encapsulation process.

Referring now to FIGS. 8A-8C, after depositing first graft layer 170 onhourglass shaped mandrel assembly 143, stent 110 may be loaded ontohourglass shaped mandrel assembly 143. One method for loading stent 110onto hourglass shaped mandrel assembly 143 is to uncouple stentretaining mandrel 134 and stent enclosing mandrel 138. When stentretaining mandrel 134 is uncoupled from stent enclosing mandrel 138, theportion of first graft layer 170 in contact with stent retaining mandrel134 and neck region 137 will remain supported by the stent retainingmandrel 134 but the portion that was in contact with stent enclosingmandrel 138 will become unsupported beyond neck region 137. As shown inFIG. 8A, by uncoupling stent retaining mandrel 134 and stent enclosingmandrel 138, stent 110 may be loaded onto stent retaining mandrel 134over first graft layer. During this step, the unsupported region offirst graft layer 170 may be manipulated in shape and guided through aninterior opening of neck region 104 and through an interior of secondflared end region 106. Where first end 153 of first graft tube 122 isused as the end of first graft layer 170, the tabs on first end 153 offirst graft tube 122 described above, may be used to help guide firstgraft layer 170 through stent 110.

Stent 110 is engaged about the stent retaining mandrel 134 byconcentrically positioning the stent 110 over first graft layer 170 andstent retaining mandrel 134. When loaded onto stent retaining mandrel134, first flared end region 102, and neck region 104 of stent 110engage with stent retaining mandrel 134 while second flared end region106 does not. Stent retaining mandrel 134 and first graft layer 170 areconfigured to have a combined diameter which is less than the innerdiameters of first flared end region 102 and neck region 104 of stent110, allowing stent to slide onto stent retaining mandrel 134.

Referring now to FIG. 8B, upon loading stent 110 on stent retainingmandrel 134 and first graft layer 170, stent enclosing mandrel 138 iscoupled to stent retaining mandrel 134, completing the hourglass shapedmandrel assembly. First graft layer 170 may be manually manipulated toavoid being damaged and prevent the occurrence of any wrinkles duringrecoupling of stent enclosing mandrel 138. For example, first graftlayer 170 may be held by the tabs described above while the stentenclosing mandrel is recoupled to the stent retaining mandrel. If firstgraft layer was taped to stent retaining mandrel 134, the tape may beremoved after recoupling. When stent enclosing mandrel 138 is coupled tostent retaining mandrel 134, stent enclosing mandrel 138 engages bothfirst graft layer 170 and second flared end region 106 of stent 110,locking stent 110 into position between large diameter end 135 and largediameter end 142. Stent enclosing mandrel 138 and first graft layer 170are configured to have a combined outside diameter which is less thanthe inner diameter of second flared end region 106 of stent 110,allowing stent 110 to slide into position on stent enclosing mandrel138. Upon placing stent 110 on first great layer 170, an optional stepinvolves applying a layer of FEP, or any other adhesive material, tofirst graft layer 170 and stent 110 for improving adhesion duringencapsulation process.

While FIGS. 5-7 illustrate one sequence for generating first graft layer170, it is appreciated that first graft layer 170 may be deposited ontoassembly apparatus 130 in different ways. For example, first graft layer170 may not be separated from first graft tube 122 until after stent 110has been loaded onto assembly apparatus 130. In this approach, afterfirst end 153 of first graft tube 122 is positioned near large diameterend 142 of stent enclosing mandrel 138 and first graft tube 122undergoes radial recoil so that the inner diameter of first graft tube122 reduces until it is met with resistance from hourglass shapedmandrel 143, as shown in FIG. 6, stent retaining mandrel 138 may beuncoupled from stent enclosing mandrel 134 Like in the sequencedescribed above, the portion of the first graft tube extending beyondneck region 137 will become unsupported after stent enclosing mandrel138 has been uncoupled. The unsupported region of first graft tube 122may then be manipulated in shape and guided through an interior openingof neck region 104 and through an interior of second flared end region106 as described above. After the stent enclosing mandrel has beenrecoupled as shown in FIGS. 8A-8B and discussed above, cuts may be madeusing cutting blades 160 and 161 to separate first graft tube 122 fromfirst graft layer 170.

In yet another example, first graft layer 170 may be deposited ontohourglass shaped mandrel 143 using an electrospinning process.Electrospinning is a process in which polymers are electrospun intoultrafine fibers which are deposited upon a target surface. Theelectrospinning process involves applying an electric force to drawfibers out of polymer solutions or polymer melts. Using electrospinning,ultrafine fibers, such as ePTFE fibers may be deposited onto hourglassshaped mandrel 143 to form first graft layer 170. Assembly apparatus maybe continuously rotated about its longitudinal axis to evenly apply theePTFE fibers. In one example, stent retaining mandrel 134 and stentenclosing mandrel 138 may be coupled together during the eletrospinningprocess. In another example, stent retaining mandrel 134 and stentenclosing mandrel 138 may be uncoupled and the conical region of stentretaining mandrel 134 including neck region 137 may be subjected to theelectrospinning process separate from the conical region of stentenclosing mandrel 138. Subsequently, when stent enclosing mandrel 138and stent retaining mandrel 134 are coupled together, the ePTFE fiberson stent retaining mandrel 134 may be sintered together to form acontinuous first graft layer 170. Second graft layer 190 may similarlybe deposited using electrospinning.

Referring now to FIG. 8C, assembly apparatus 130 may be configured suchthat first graft tube 122 and second graft tube 124 may be loaded ontoassembly apparatus 130 from the side closest to stent enclosing mandrel138. As discussed above, stent enclosing mandrel 138 may be removablycoupled to handle segment 144. In the alternative configuration shown inFIG. 8C, stent enclosing mandrel 138 may be uncoupled from handlesegment 144 and tapered dilation mandrel 131′ may be coupled to stentenclosing mandrel 138 instead. It will be understood by those in the artthat the couplings are interchangeable and may be any of a wide varietyof suitable couplings. Tapered dilation mandrel 131′ has first end 132′and second end 133′ wherein the diameter of second end 133′ is greaterthan the diameter of first end 132′ and the diameter of second end 133′is equal to the diameter of large diameter end 142 of stent enclosingmandrel 138. In the configuration shown in FIG. 8C, large diameter end135 may also perform as handle segment 144′ for pushing.

Using the configuration shown in FIG. 8C, an axial force 165 may beapplied to assembly apparatus 130 to cause tapered dilatation mandrel131′ having first end 132′ to pass into and through the lumen of thefirst graft tube 122. Similarly, axial force 165 may be applied toassembly apparatus 130 to guide assembly apparatus 130, and specificallyfirst end 132′, into stent 110 which is configured to expand as tapereddilatation mandrel 131′ is pushed into stent 110. Axial force 165 may beapplied by using handle segment 144′ to push assembly apparatus 130. Byengaging first end 132′ with expandable stent 110 exhibiting springtension, stent 110 may be dilated as it moves along tapered dilatationmandrel 131′. In this manner, first end region diameter D1, second endregion diameter D2, and neck diameter D3 of stent 110, as shown in FIG.1, may be expanded to a diameter equal to or larger than large diameterend 142 of stent enclosing mandrel 138, thus permitting stent 110 totraverse large diameter end 142. As stent 110 exhibiting spring tensionis passed over hourglass shaped mandrel assembly 143, it encounters noresistance to radial recoil and thus radially recoils into position overfirst graft layer 170 and between large diameter end 135 and largediameter end 142. Alternatively, stent 110 may be expanded to a slightlylarger diameter than second diameter end 142 by applying a radiallyexpansive force on stent 110 using an external expansion tool. In thisexample, after expanding stent 110 to the appropriate diameter, stent110 may be concentrically placed over stent enclosing mandrel 138 andallowed to radially recoil into position over hourglass shaped mandrel143 having first graft layer 170 deposited on top.

In yet another alternative arrangement, stent enclosing mandrel 138 mayalternatively be comprised of a cylindrical region instead of a conicalregion. The cylindrical region may have the same diameter as neck region137 such that the cylindrical region of stent enclosing mandrel 138 mayappear as an extension of neck region 137 when stent enclosing mandrel138 is coupled to stent retaining mandrel 134. In this alternativeembodiment, stent enclosing mandrel 138 also may be coupled to tapereddilation mandrel 131′ which may have second end 133′ that is equal indiameter to neck region 137 and smaller in diameter than first end 131′.Stent enclosing mandrel 138 having the cylindrical region instead of aconical region, may be used to encapsulate a stent having a conicalregion and a neck region that forms a conduit. Any of the methods andtechniques described herein to encapsulate the hourglass shaped stentmay be used to encapsulate the stent having the cylindrical regioninstead of the conical region. Upon completion of encapsulation, theencapsulated stent may be gently removed from assembly apparatus 130 bysliding the encapsulated stent over the tapered dilation mandrel 132′.Alternatively, stent enclosing mandrel 138 may be uncoupled from stentretaining mandrel 134.

FIGS. 9-11 represent sequential views of the second graft tube 124 beingloaded onto the tapered dilation mandrel 131 and being concentricallyengaged about the stent member 110. Engagement of second graft tube 124over tapered dilation mandrel may be facilitated by forming tabs onfirst end 171 of second graft tube 124 similar to the method describedabove, involving cutting longitudinal slits (not shown) alongdiametrically opposed sides of the graft member. The tabs can then beused to retain the second graft tube 124 while axial force 170 isapplied to assembly apparatus 130. Alternatively, the tabs may be usedto manually pull second graft tube 124 over tapered dilation mandrel 131and hourglass shaped mandrel assembly 143.

Referring now to FIG. 9, second graft tube 124 may be engaged withtapered dilatation mandrel 131 in much the same way as first graft tube122—by applying axial force 180 to assembly apparatus 130 which causesthe tapered dilatation mandrel to pass into and through lumen 173 ofsecond graft tube 124. As second graft tube 124 passes over second end133 of tapered dilatation mandrel 131, the inner diameter of secondgraft tube 124 is radially expanded to that of the outer diameter ofsecond end 133 of tapered dilation mandrel 131. The assembly apparatus130 is passed into and through lumen 173 of second graft tube 124 untilfirst end 171 of second graft tube 124 is close to large diameter end142 of stent enclosing mandrel 138. As second graft tube moves axiallyover stent 110 and to a position over large diameter end 142 of stentenclosing mandrel 138, second graft tube 124 undergoes radial recoil sothat the inner diameter of second graft tube 124 reduces until it is metwith resistance. As illustrated in FIG. 10, second graft tube 124 isradially recoiled onto stent 110. Second graft tube 124 also may beradially recoiled into cutting crevices 151 and 152.

Alternatively, second graft tube 124 may be positioned onto stent 110via an assembly apparatus 130 that is configured to expand and/orcontract radially. Assembly apparatus may be comprised of materialhaving expansion properties or contraction properties which may beresponsive to exterior conditions. For example, hourglass shaped mandrelassembly 143 may be compressible by applying a force normal to thesurface of hourglass shaped mandrel 143. Instead, assembly apparatus 130may be comprised of material having a high coefficient of thermalexpansion permitting the hourglass shaped assembly to contract whenplaced in a low temperature environment and expand when placed in a hightemperature. Alternatively, assembly apparatus may have a rigid core andmultiple surfaces that move independently from one another, the surfacesbeing connected to the core by a number of springs that are configuredto permit movement of the surfaces relative to the core when a normalforce is applied to the surfaces. For example, a surface may compresstowards the core when a normal force is applied and the same surface mayexpand radially out from the rigid core when the normal force isreleased. In addition, or alternatively, the core of the assemblyapparatus 130 may have a screw assembly embedded within the core andconfigured to translate a rotational force applied to the screw assemblyinto a radial force which is applied to the surfaces to push thesurfaces radially outward, or pull the surfaces radially inward.

Expandable stent 110 having spring tension may be positioned oncompressible hourglass shaped mandrel assembly 143 and stent andassembly together may be compressed when a compressive radial force isapplied. At a certain compressive force, first end region diameter D1and second end region diameter D2 of stent 110 may be compressed to neckdiameter D3. In this compressed state, second graft tube 124 may beeasily moved axially over compressed stent 110 and first graft layer170. Subsequent to positioning second graft tube 124 over compressedstent 110 and first graft layer 170, compressive force applied to stent110 and compressible hourglass shaped mandrel assembly 143 may bereleased. At the same time, hourglass shaped mandrel assembly 143 mayexpanded. In this way second graft tube 124 may be engaged with stent110.

FIGS. 10 and 11 illustrate the steps for separating second graft tube124 from stent-graft assembly 120. After depositing second graft tube124 on stent 110, cutting blades 160 and 161 may again be used to makecircumferential cuts in second graft tube 124 at a position near thelarge diameter ends of stent retaining mandrel 134 and stentencompassing mandrel 138. For example, cutting blades 160 and 161 maymake circumferential cuts at the position of cutting crevices 151 and152. As explained above, cutting crevices 151 and 152 may be positionedat a length longer than the length of stent 110 to account for recoil ofgraft material upon being cut. After cutting second graft tube 124 withcutting blades 160 and 161, second graft layer 190 is deposited ontostent 110 which is positioned over graft layer 170. Second graft layer190 has a length longer than stent 110. As such, a section of secondgraft tube 124 extends beyond opposing ends of stent 110 and is similarin length to first graft layer 170. Waste portion of second graft tube124 remaining on assembly apparatus 138 may be discarded. Where stent110 is only partially encapsulated, first graft layer 170 and/or secondgraft layer 190 may have a length shorter than stent 110 and thus maynot extend beyond opposing ends of stent 110. For example, only firstflared end region 102 or second flared end region 106 may beencapsulated. Where stent 110 takes a different asymmetric shape, suchas an hourglass shape on one side and a straight tube shape on the otherside, only one portion of asymmetric stent 110 may be encapsulated.

To securely bond first graft layer 170 to second graft layer 190,pressure and heat may be applied the stent-graft assembly to achievesintering. Sintering results in strong, smooth, substantially continuouscoating that covers the inner and outer surfaces of the stent. Sinteringmay be achieved by first wrapping the ends of first graft layer 170 andsecond graft layer 190 with strips of tape such as TFE or ePTFE tape tosecure the stent-graft assembly to the mandrel. To apply pressure,stent-graft assembly 120 attached to assembly apparatus 130 may beplaced in a helical winding wrapping machine which tension wraps thestent-graft assembly 120 with at least one overlapping layer of tape.For example, stent-graft assembly 120 may be wrapped with a singleoverlapping layer of ½ inch ePTFE tape with an overlap of the winding ofabout 70%. The force exerted by the TFE or ePTFE wrapping tapecompresses the stent-graft assembly against the hourglass shaped mandrelassembly 143, thereby causing the graft layers to come into intimatecontact through interstices of stent 110. In stent 110 shown in FIG. 1,interstices exist in the between the struts and sinusoidal rings.Varying tape thickness may reduce or improve ePTFE conformance. Forexample, thicker tape may result in more compression uniformity thanthinner tape material.

Stent-graft assembly 120 attached to assembly apparatus 130 may then beheated by placing the stent-graft assembly and assembly apparatus into aradiant heat furnace. For example, stent-graft assembly 120 may beplaced into a radiant heat furnace which had been preheated. In oneexample, sintering may be achieved at 327° C. The humidity within theradiant heat furnace may preferably be kept low. The stent-graftassembly may remain in the radiant heat furnace for a time sufficientfor first graft layer 170 to sinter to second graft layer 190. In oneexample, stent-graft assembly 120 may remain in the furnace for about7-10 minutes. The heated assembly may then be allowed to cool for aperiod of time sufficient to permit manual handling of the assembly.After cooling, the helical wrap may be unwound from stent-graft assembly120 and discarded. The encapsulated stent may then be concentricallyrotated about the axis of the mandrel to release any adhesion betweenthe first graft layer 170 and hourglass shaped mandrel assembly 143. Theencapsulated stent, still on the mandrel, may then be placed into alaser trimming fixture to trim excess graft materials away fromstent-graft assembly 120. In addition, the encapsulated stent may betrimmed at various locations along the stent such as in the middle ofthe stent, thereby creating a partially encapsulated stent.

Alternatively, first graft layer 170 may be sintered to second graftlayer 190 by inducing pressure. For example, assembly apparatus 130 orat least hourglass shaped mandrel assembly 143 may have smallperforations which may be in fluid communication with a vacuum pumpsituated in an inner lumen of assembly apparatus 130 or otherwise influid communication with an inner lumen of assembly apparatus 130.Additionally or alternatively, the assembly apparatus 130 may be placedin a pressurized environment that is pressurized using a compressorpump, for example. In another example, a balloon such as a Kevlarballoon may also or alternatively be applied to the exterior of thestent-graft assembly to apply pressure to the stent-graft assembly. Viathe pressure applied, the first graft layer 170 may collapse on thesecond graft layer 190 forming even adhesion. A combination of bothpressure and heat may also be used to sinter the first graft layer 170to the second graft layer 190. Trimming may then take place in the samemanner as described above.

After trimming excess graft materials, stent-graft assembly 120 may beremoved by decoupling stent retaining mandrel 134 from stent enclosingmandrel 138. Upon decoupling stent retaining mandrel 134 and stentenclosing mandrel 138, stent-graft assembly 120 remains supported bystent retaining mandrel 134. Stent-graft assembly 120 may then beremoved from stent retaining mandrel 134 by axially displacingstent-graft assembly 120 relative to stent retaining mandrel 134.

Upon removal of stent-graft assembly 120 from assembly apparatus 130,stent-graft assembly 120 may be manipulated to a reduced first endregion diameter D1, second end region diameter D2 and neck regiondiameter D3. The assembly stent-graft assembly may achieve these smallerdiametric dimensions by methods such as crimping, calendering, folding,compressing or the like. Stent-graft assembly 120 may be constrained atthis dimension by disposing stent-graft assembly 120 in a similarlysized cylindrical sheath. Once positioned in the sheath, stent-graftassembly 120 may be delivered to an implantation site using a catheterbased system including a delivery catheter. The catheter based systemmay further comprise an engagement component for temporarily affixingstent-graft assembly 120 to the delivery catheter. The engagementcomponent may be configured to disengage the stent-graft assembly 120from the delivery catheter when stent-graft assembly 120 has reached thedelivery site. At the delivery site, the sheath may be removed torelease the constraining force and permit the intraluminal stent toelastically expand in the appropriate position.

While the approach set forth above describes depositing a layer ofbiocompatible material on an interior surface of stent 110 and anexterior surface of stent 110, it is understood that the stent 110 maybe coated with only one layer of biocompatible material. For example,stent 110 may be engaged with only first graft layer 170 along aninterior surface, following only the appropriate steps set forth above.Alternatively, stent 110 may be engaged with only second graft layer 190along an exterior surface, following only the appropriate steps setforth above.

As explained above, stent 110 may be comprised of a plurality ofsinusoidal rings connected by longitudinally extending struts. However,it is understood that stent 110 may be constructed from a plurality ofinterconnected nodes and struts having varying distances and formingvarious shapes and patterns. In one embodiment the inter-nodal-distance(IND) of stent 110 may be manipulated by controlling the tension of thebiocompatible material layers during encapsulation. For example, thestent may be encapsulated in a manner providing different pulling forceson stent 110. This may enable different functionality of various areasof the encapsulated stent which are known to be influenced by IND. Inone example, by controlling tension of the biocompatible material layersduring encapsulation, different functionality of various areas withrespect to tissue ingrowth characteristics may be achieved. Further, itis understood that encapsulation may be performed such that stent 110 isconstrained in a restricted or contracted state by the encapsulationmaterial. For example, the neck diameter may be decreased from 6 mm to 5mm. This may permit controlled in-vivo expansion to a fully expandedstate using, for example, balloon inflation, whereby the constraint isremoved. This procedure may be beneficial in a case where a clinicalcondition dictates an initial restricted state for delivery but requiresa larger unconstrained state for implantation or treatment.

Referring now to FIGS. 12A-D, an alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated.FIGS. 12A-D represent sequential views of first graft tube 122 andsecond graft tube 124 being loaded onto and concentrically engaged aboutstent graft assembly 120. As shown in FIG. 12A the process may start byengaging first graft tube 122 over stent 110. Stent 110 may be crimpedto a diameter smaller than first graft tube 122 and guided into grafttube 122. Alternatively, or in addition to, first graft tube 122 may bestretched to a diameter slightly larger than stent 110 using anexpanding mandrel or other stretching technique and guided over stent110.

Upon positioning first graft tube 122 over stent 110, second graft tube124 may be positioned within and along the entire length of stent 110,shown in FIG. 12B. Second graft tube 124 may be pulled through stent 110while stent 110 remains engaged with first graft tube 122. Subsequently,as shown in FIG. 12C, female mandrel 195 may be introduced near secondflared end region 106 of stent 110. Female mandrel 195 may have asimilar shape as second flared end region 106 only with slightly smallerdimensions. Female mandrel 195 may have receiving portion 196 designedto receive male mandrel 197. Having a conical shape, female mandrel 195may be gently advanced within second graft tube 124 until female mandrel195 takes up nearly the entire space within second flared region 106. Inthis manner, second graft tube 124 may be engaged with stent 110 alongan interior surface of second flared region 106 and in some embodimentsneck region 104.

Referring now to FIG. 12D, male mandrel 197 may be introduced near firstflared end region 102. Male mandrel 197 may be similar in shape to firstflared end region 102 only with slightly smaller dimensions. Malemandrel 195 may have protruding section 198 sized and shaped to bereceived by female mandrel 195. Having a conical shape, male mandrel 197may be gently advanced within second graft tube 124 toward femalemandrel 195 until female assembly 195 takes up nearly the entire spacewithin first flared region 102 and protruding section is fully receivedby receiving portion 196. In this manner, second graft tube 124 may beengaged with stent 110 along an interior surface of second flared region106 and in some embodiments neck region 104.

Upon engaging female mandrel 195 and male mandrel 197, stent 110 may beentirely covered on an exterior surface by first graft tube 122 andentirely covered on an interior surface by second graft tube 124. Firstgraft tube 122 and second graft tube 124 may be appropriately cut awayaccording to the same procedures illustrated in FIGS. 6 and 10 resultingin first graft layer 170 and second graft layer 190. Further, stentgraft assembly 120 may be produced using the same procedures detailedabove including the procedures for securely bonding first graft layer170 to second graft layer 190 involving pressure and heat applied to thestent-graft assembly to achieve sintering. It is understood that themandrel placed in the first flared region 102 may alternatively be afemale mandrel and the mandrel placed in second flared region 106 mayalternatively be a male mandrel. It is also understood that the processdepicted in FIGS. 12A-D may start first with the mandrel entering thefirst flared region 102 of stent 110.

Referring now to FIGS. 13A-13E, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 13A, first graft layer 170 may be pre-formed into anhourglass shaped pre-shaped first graft layer 199 using a dedicatedmandrel and heat treatment. The pre-formed shape may have dimensionssimilar to that of stent 110. Upon forming pre-shaped first graft layer199, female mandrel 200 may be introduced into one side of pre-shapedfirst graft layer 199, such that female mandrel 200 takes up nearly theentire space within one hourglass side of pre-shaped first graft layer199 as shown in FIG. 13B. Female mandrel 200 may have receiving portion201 designed to receive male mandrel 203.

Upon placing female mandrel 200 within pre-formed first graft layer 199,stent 110 may be placed over pre-shaped first graft layer 199, as showin in FIG. 13C. Stent 110 may be positioned over first graft layer 199or first graft layer 199 may be positioned within stent 110. Stent 110,having a shape similar to that of pre-formed first graft layer 199should fit into place on pre-formed first graft layer 199.

Once stent 110 is deposited on pre-shaped first graft layer 199, secondpre-shaped graft layer 202, formed into an hourglass shape havingdimensions similar to stent 110 may be deposited on stent 110 as isillustrated in FIG. 13D. Pre-shaped second graft layer 202 may be formedin a similar manner as pre-shaped first graft layer 199, using adedicated mandrel and heat treatment. Pre-shaped second graft layer 202may be expanded and positioned over stent 110. Pre-shaped second graftlayer 202, may recoil into its pre-shaped form upon releasing any radialexpansion force on pre-shaped second graft layer 202. Alternatively, orin addition to, stent 110 may be crimped to facilitate mounting ofsecond graft layer 202.

Referring now to FIG. 13E, male mandrel 203 may be introduced near theend of pre-formed first graft layer 199 not occupied by female mandrel200. Male mandrel 203 may be similar in shape to this end of pre-formedfirst graft layer 199 only with smaller dimensions. Male mandrel 203 maybe have protruding section 204 sized and shaped to be received byreceiving portion 201 of female mandrel 200. Having a conical shape,male mandrel 203 may be gently advanced within pre-formed first graftlayer 199 toward female mandrel 200 until protruding section 204 isfully received by receiving portion 201.

Upon engaging female mandrel 200 and male mandrel 203, stent 110 may beat least partially covered on an exterior surface by pre-shaped secondgraft layer 202 and at least partially covered on an interior surface bypre-shaped first graft layer 199. Stent graft assembly 120 may beproduced using the same procedures detailed above including theprocedures for securely bonding first graft layer 170, in this casepre-shaped first graft layer 199, to second graft layer 190, in thiscase pre-shaped second graft layer 202. These procedures may involvepressure and heat applied to the stent-graft assembly to achievesintering. This process simplifies the mounting of the graft tubes andreduces risk of tears and non-uniformities. It is understood that themandrel inserted first into pre-formed first graft layer 199 mayalternatively be a male mandrel and the mandrel inserted second mayalternatively be a female mandrel.

Referring now to FIGS. 14A-14D, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 14A, the process may start by engaging first graft tube122 over stent 110. Stent 110 may be crimped using dedicated crimpingtools, such as ones detailed in U.S. Patent Publication No. 2014/0350565to a diameter smaller than first graft tube 122 and guided into grafttube 122. Alternatively, or in addition to, first graft tube 122 may bestretched to a diameter slightly larger than stent 110 using anexpanding mandrel or other stretching mechanism and guided over stent110. The approach illustrated in FIG. 14A may achieve a firm engagementbetween crimped stent 110 and the first graft layer 170, enablingimproved encapsulation.

Upon positioning first graft tube 122 over stent 110, second graft tube124 may be positioned within and along the entire length of stent 110,shown in FIG. 14B. Second graft tube 124 may be pulled through stent 110while stent 110 remains engaged with first graft tube 122.Alternatively, stent 110, with first graft tube 122 engaged with stent110 may be expanded, using well-known expansion techniques, andpositioned over second graft tube 124. Subsequently, as shown in FIG.14C, balloon catheter 205 having inflatable balloon 206 may be insertedinto second graft tube 124 such that the balloon catheter 205 issurrounded by stent 110 and first graft layer 122. Alternatively, secondgraft tube 124 may be positioned over inflatable balloon 206 andinflatable balloon 206 may be positioned within stent 110 via ballooncatheter 205.

Referring now to FIG. 14D, upon positioning balloon catheter 205 intosecond graft tube 124, inflatable balloon 206 of balloon catheter 205may be inflated to engage second graft tube 124 with an interior surfaceof stent 110. Using inflatable balloon 206 to engage second graft layer124 with stent 110 permits uniform contact between and engagementbetween second graft tube 124 and stent 110 as well as second graft tube124 and first graft layer 122 between the interstices of stent 110, thusoptimizing the adhesion during encapsulation. The degree of inflationmay be manipulated to achieve a desired pressure within the balloon anda desired adhesion between first graft tube 122 and the second grafttube 124. Additionally, the degree of inflation may be manipulated toachieve a desired inter-nodal-distance of the graft material. Differentpressures may also be achieved by varying the wall thickness of theballoon. Furthermore, interlocking balloons may be used to reduce bondlines.

First graft tube 122 and second graft tube 124 may be appropriately cutaway according to the same procedures illustrated in FIGS. 6 and 10resulting first graft layer 170 and second graft layer 190. Further,stent graft assembly 120 may be produced using the same proceduresdetailed above including the procedures for securely bonding first graftlayer 170 to second graft layer 190 involving pressure and heat appliedto the stent-graft assembly to achieve sintering.

Referring now to FIGS. 15A-15F, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 15A, the process may start by placing stent 110 withinfunnel 207 and advancing stent 207 within funnel 207 towards a reducedsection of funnel 207, using, for example, a dedicated pusher tool likethe one described in U.S. Patent Publication No. 2014/0350565, to reducethe diameter of stent 110. Stent 110 may be constructed in a mannerthat, upon reduction caused by funnel 207, the shape of stent 110 morphssuch that the flared ends are tapered and eventually turned inwardtoward a longitudinal axis of stent 110, resulting in stent 110 having asubstantially reduced cross-sectional diameter.

As is shown in FIG. 15B, funnel 207 may have introducer tube 208extending from the narrow side of the funnel 207 which may receive stent110 after stent 110 has been fully restricted by funnel 207. Introducertube 208 may have a diameter smaller than that of first graft tube 122.Introducer tube may thus be inserted into first graft tube 122, as isillustrated in FIG. 15C, and stent 110 having the reduced diameter, maybe advanced out of introducer tube 208 and into first graft tube 122.

Referring now to FIG. 15D, stent 110 is illustrated after having beenadvanced from introducer tube 208 and into first graft tube 124. As isshown in FIG. 15D, upon the removal of inward radial force fromintroducer tube 208, stent 110 may expand radially to a diameter largerthan the diameter of first graft tube 122, thereby engaging first grafttube 122 along the outer surface of stent 110. An end of first grafttube 122 may have been positioned a distance beyond introducer tube 208such that upon depositing stent 110 into first graft tube 122, remainingportion 209 of first graft tube 122 extends beyond stent 110 a distanceof more than one length of stent 110.

Referring now to FIG. 15E, remaining portion of first graft tube 122 maybe used as a second graft layer along the internal surface of stent 110by pushing remaining portion 209 through the interior of stent 110 andout an opposing side of stent 110, in the direction indicated by thearrows in FIG. 15D. In this manner, first graft layer 122 may extendalong an exterior surface of stent 110, curve around an end of stent 110and travel along the interior of stent 110.

To engage remaining portion 209 with the interior surface of stent 110,female mandrel 200 having receiving portion 201 and male mandrel 203having protruding section 204 may be inserted into the stent-graftcombination. Female mandrel 200 may be introduced first to one end ofthe stent-graft combination having a size slightly larger than thedimensions of female mandrel 200. Subsequently, male mandrel 203 may beintroduced into the opposing end of the stent-graft combination andadvanced until protruding section 204 is received by receiving section201. As female mandrel 200 and male mandrel 201 are inserted, stent 110may be guided into its original hour-glass shape. This method may induceimproved adhesion between first graft tube 122, remaining portion 209and stent 110.

Upon engaging female mandrel 200 and male mandrel 203, first graft tube122 and remaining portion 209 may be appropriately cut away according tothe same procedures illustrated in FIGS. 6 and 10 resulting first graftlayer 170 and second graft layer 190, with the exception that only oneside of stent graft assembly needs to be cut or otherwise removed firstgraft tube 122 and remaining portion 209. Stent graft assembly 120 maybe produced using the same procedures detailed above including theprocedures for securely bonding first graft layer 170 to second graftlayer 190 involving pressure and heat applied to the stent-graftassembly to achieve sintering. It is also understood that the processdepicted in FIGS. 15F may start with the male mandrel entering the stentgraft combination first.

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. For example, assembly mandrel 130 may include additional orfewer components of various sizes and composition. Furthermore, whilestent encapsulation is described herein, it is understood that the sameprocedures may be used to encapsulate any other bio-compatible material.The appended claims are intended to cover all such changes andmodifications that fall within the true spirit and scope of theinvention.

What is claimed is:
 1. A method for making an encapsulated stent-graft,the method comprising: providing an expandable stent having a firstflared end and a second flared end, the expandable stent defining alumen therethrough and having a first surface and a second surfaceopposite the first surface; providing a graft tube having a length overtwice the expandable stent's length; engaging a first portion of thegraft tube with the first surface of the expandable stent; curving asecond portion of the graft tube around the first or second flared endof the expandable stent; and engaging the second portion of the grafttube with the second surface of the expandable stent for encapsulationto make the encapsulated stent-graft.
 2. The method of claim 1, whereinengaging a first portion of the graft tube with the first surface of theexpandable stent comprises inserting the expandable stent into a firstend of a funnel and advancing the expandable stent towards a second endof the funnel, the second end of the funnel coupled to the graft tubeand having a smaller diameter than the first end of the funnel.
 3. Themethod of claim 2, wherein advancing the expandable stent towards asecond end of the funnel reduces the diameter of the expandable stent.4. The method of claim 2, wherein engaging a first portion of the grafttube with the first surface of the expandable stent further comprisesadvancing the expandable stent into the graft tube such that a firstportion of the graft tube engages with at least a portion of the firstsurface of the expandable stent.
 5. The method of claim 4, furthercomprising withdrawing the funnel such that the expandable stentexpands.
 6. The method of claim 1, further comprising inserting a firstmandrel into the first flared end of the expandable stent such that atleast a portion of the second portion of the graft tube is disposedbetween the first mandrel and the first flared end of the expandablestent, the first mandrel sized and shaped to fit within the first flaredend of the expandable stent.
 7. The method of claim 6, furthercomprising inserting a second mandrel into the second flared end of theexpandable stent such that at least a portion of the second portion ofthe graft tube is disposed between the second mandrel and the secondflared end of the expandable stent, the second mandrel sized and shapedto fit within the second flared end of the expandable stent.
 8. Themethod of claim 7, further comprising removably coupling the firstmandrel to the second mandrel.
 9. The method of claim 8, wherein thefirst mandrel has a receiving portion and the second mandrel has aprotruding portion sized and shaped to fit within the receiving portion.10. The method of claim 9, wherein the first mandrel comprises a firstconical region having a flared end with a first diameter and an apex endwith a second diameter; and the second mandrel comprises a secondconical region having a flared end with a third diameter and an apex endwith a fourth diameter.
 11. The method of claim 10, wherein removablycoupling the first mandrel to the second mandrel comprises aligning thefirst mandrel with the second mandrel such that the apex ends of thefirst mandrel and the second mandrel contact one another.
 12. The methodof claim 7, further comprising compressing the stent-graft against themandrel to form the encapsulated stent.
 13. The method of claim 12,wherein compressing the stent-graft comprises winding a layer of tapeover the graft tube to compress the stent-graft against the mandrel. 14.The method of claim 1, further comprising heating the graft tube engagedwith the expandable stent.
 15. The method of claim 14, wherein theexpandable stent comprises through-wall openings; and wherein heatingthe graft tube engaged with the expandable stent causes the firstportion and the second portion of the graft tube to bond to one anotherthrough the through-wall openings.
 16. The method of claim 15, whereinheating the graft tube engaged with the expandable stent causes thefirst portion and the second portion of the graft tube to becomesintered together to form a monolithic layer of biocompatible material.17. The method of claim 1, further comprising applying pressure to thegraft tube engaged with the expandable stent.
 18. The method of claim 1,wherein the first surface of the expandable stent is the expandablestent's outer surface.
 19. The method of claim 1, wherein the secondsurface of the expandable stent is the expandable stent's inner surface.20. The method of claim 1, wherein the expandable stent comprises metaland the graft tube comprises expanded polytetrafluoroethylene (ePTFE).